Radioactivity of Blood Samples Taken from Thyroidectomized Thyroid Carcinoma Patients After Therapy with 131I

Background: Occasionally, blood samples may be required from thyroid cancer patients after they have been given the therapy dose of I-131, as part of necessary medical management of comorbidities. Thus, in the days after I-131 administration, medical health professionals may be involved in the withdrawal, handling, and manipulation of radioactive blood samples. The purpose of this study was to quantify the amount of radioactivity in blood samples taken from thyroidectomized thyroid carcinoma patients after the administration of therapeutic activities of I-131. Methods: For dosimetry purposes, serial blood sampling is performed on thyroidectomized thyroid carcinoma patients prior to therapy with I-131. The quantities of radioactive material present in these blood samples were expressed as a percentage of the administered activity and then extrapolated to the high levels of I-131 used in therapy for 377 patients in this study. The corresponding radiation exposure rate from the blood samples was then calculated to determine what radiation protection methods were required for staff handling these samples. Results: The average amount of radioactivity in a 1 mL blood sample at 1 hour postadministration of 5.5 GBq (150 mCi) of I-131 was 0.2 +/- 0.15MBq (5.4 +/- 4.0 mu mCi). This corresponds to an exposure rate of 1.23 mu mSv/h (0.123 mrem/h) at 10 cm from the sample. For samples obtained beyond 24 hours after a therapeutic administration of 5.55 GBq (150 mCi), the exposure levels are approximately equal to background radiation. Conclusion: The data in this study indicate that the radiation exposure from blood samples withdrawn from thyroidectomized thyroid cancer patients is low. However, to ensure that staff members are exposed to minimal levels of radiation, it is imperative that staff members who are involved in withdrawing, handling, or manipulating radioactive blood samples adhere to the recommended radiation safety practices.